A new report on the U.S. drone missile strike that killed 12 members of a Yemeni wedding convoy has renewed calls for the Obama administration to make public its own investigations into the incident — and explain how such strikes are consistent with international laws of war.

The detailed, 28-page report from Human Rights Watch describes conflicting accounts of the December 12 attack, but nevertheless concludes that some, if not all, of the victims may have been civilians.

The laws of war prohibit attacks on civilians that are not discriminate or attacks that cause civilian loss disproportionate to the expected military advantage.

The report also calls on the U.S. government to explain how the attack could possibly have complied with the new policies President Obama announced in May 2013, and repeated less than three months before the wedding strike, that he had “limited the use of drones so they target only those who pose a continuing, imminent threat to the United States where capture is not feasible, and there is a near certainty of no civilian casualties.”

Obama administration officials have insisted since the strike that only members of al Qaeda were killed. Defense Department spokesman Bill Speaks reiterated to TheIntercept on Wednesday “that the Yemeni Government has stated that the targets of this operation were dangerous senior al Qaeda militants,” but he declined to provide any details or evidence to support that conclusion. National Security Council spokeswoman Caitlin Hayden also declined.

The Associated Press reported Thursday morning that, according to three anonymous U.S. officials, two government investigations concluded that only members of al Qaeda were hit in the strike:

Lt. Gen. Joseph Votel, commander of Joint Special Operations Command, ordered an independent investigation by an Air Force general and the White House requested another by the National Counterterrorism Center. Both concluded no civilians were killed. Votel’s staff also showed lawmakers video of the operation. Two U.S. officials who watched the video and were briefed on the investigations said it showed three trucks in the convoy were hit, all carrying armed men.

But the officials provided no details, no evidence — and were not quoted by name. The AP explained:

The officials said the Pentagon can’t release details because both the U.S. military and the CIA fly drones over Yemen. By statute, the military strikes can be acknowledged, but the CIA operations cannot. The officials said that if they explain one strike but not another, they are revealing by default which ones are being carried out by the CIA.

But at its core, the Human Rights Watch report makes the case that a swirling mix of competing accounts surrounding the strike demands a transparent investigation and publicly available findings. In an interview with The Intercept Wednesday, Letta Tayler, the author of the report, said the contradictory claims her team uncovered investigating the strike were “mind boggling.”

“It would be comical if we were not talking about human beings who were killed and yet, that is what we’re talking about,” Tayler said. “And that’s why the silence is unconscionable.”

“The contradictory accounts that we documented cry out for an official explanation,” she added. “The families of those killed deserve to know what happened and why the U.S. turned this wedding procession into a funeral.”

Tayler said her organization has “serious questions about how intelligence is gathered in Yemen and how it is being used.” But, she noted: “We do not know if faulty intelligence led to this strike or not, because we do not know enough about the strike itself.”

A Feb. 10 article in The Intercept described the National Security Agency’s role in locating targets for lethal drone strikes, raising concerns that the U.S. has been overly relying on the activity of mobile phones that targets are believed to be using, rather than confirming a target’s identity with operatives or informants on the ground. A former Joint Special Operations Command (JSOC) drone operator and NSA analyst told The Intercept that during his time in Yemen, the U.S. gathered “almost zero” human intelligence before strikes. “Every one of their strikes relies on signals and imagery for confirmation,” he said.

The level of detail in the Human Rights Watch report impressed close observers of the U.S. drone program. Micah Zenko, Douglas Dillon Fellow at Council on Foreign Relations and a leading expert on U.S. targeted killings, told The Intercept, “It’s just a very careful and cautious study.” He said the report “raises incredibly troubling evidence” that “the United States might have blown it…might have killed civilians unintentionally.”

“The report is well documented and it is carefully measured in saying what the researchers know and don’t know,” Ryan Goodman, law professor at New York University and co-editor-in-chief of the national security blog, JustSecurity.org, said in an email to The Intercept. “Of course mistakes happen in wartime, but a key question for the laws of war is whether the mistake resulted from a failure to take the proper precautions,” Goodman added. “The report includes evidence that clearly suggests violations of the laws of war may have occurred.”

The attack took place late in the afternoon of December 12, 2013. According to the report, four Hellfire missiles slammed into a convoy of 11 cars stopped by a flat tire. The cars, Human Rights Watch confirmed, were carrying 50 to 60 wedding-goers. They had been traveling from the bride’s home to the groom’s village.

Abdullah Muhammad al-Tisi, a local sheikh, was driving one of the vehicles. “Everyone was happy; everyone was celebrating the wedding,” he told Human Rights Watch. “Then the strike turned happiness to grief.”

Al-Tisi said he watched as four men piled out of 2005 Toyota Hilux pickup truck ahead of him and ran. Moments later a missile tore into the vehicle. Soon after, three more missiles rained down, throwing shards of hot metal through the air.

“Blood was everywhere, the bodies of the people who were killed and injured were scattered everywhere,” al-Tisi, a father of three, recalled. “I saw the missile hit the car that was just behind the car driven by my son. I went there to check on my son. I found him tossed to the side. I turned him over and he was dead. He was struck in his face, neck, and chest.”

In addition to the 12 men who died, 15 others were wounded. Shrapnel cut the bride’s face and tore her clothing. Roughly half the wedding party was killed or wounded. The youngest man to die was 20, the oldest 65.

Anonymous U.S. officials told reporters the military’s elite JSOC operatives carried out the strike — not the CIA.

The day after the attack, Yemen’s official news news agency cited an unnamed “official source” who claimed that a car belonging to an al Qaeda “leader” that was carrying “many terrorist members and leaders who were involved in plotting attacks against armed forces, police, and vital public facilities” had been targeted. There was no mention of civilian casualties until the following day, when a Yemeni general apologized for the attack at a local community meeting. The general said the attack was a “mistake,” and provincial officials paid the families a total of $159,000 in reparations and gave them 101 Kalashnikov assault rifles, a tribal gesture of apology.

Human Rights Watch found three government sources who disputed the official news agency account of the strike. Those sources said five civilians were killed in the attack. None of the Yemeni sources said who among the dead was al Qaeda and who was a civilian wedding celebrant. One of the sources did say, however, that the dead included, “smugglers and arms dealers. They were guys for hire — shady.”

Unnamed U.S. officials later told the AP that the target was Shawqi Ali Ahmad al-Badani, a member of al Qaeda in the Arabian Peninsula (AQAP), who they said was one of Yemen’s most wanted terrorists and a key figure in the plot that resulted in the closure of 22 U.S. diplomatic posts the preceding summer. The officials claimed he was wounded in the strike but escaped.

Human Rights Watch found two Yemeni government sources who claimed the first vehicle struck by the American missile was al-Badani’s and that he did indeed escape. Two other Yemeni sources, however, said he was residing in a city more than 100 miles from the scene of the strike.

Witnesses and relatives told Human Rights Watch they did not know al-Badani and that he was most certainly not at the wedding. Other sources who spoke to the human rights organization claimed an entirely different AQAP member – Nasr al-Hotami – was in the truck that was fired upon. Again, relatives denied the claim. Some Yemeni officials suggested AQAP “had joined the procession, possibly as ‘camouflage.'”

“The conflicting accounts, as well as actions of relatives and provincial authorities, suggest that some, if not all those killed and wounded were civilians,” the report concludes.

Tayler, the report’s author, said the strike invites questions that have become frustratingly commonplace for U.S. drone strike investigators.

“How do the laws of war apply here? How can you assume that civilian loss will not be disproportionate to the expected military advantage if you are striking a wedding convoy?” she said. “There may be an answer but the U.S. sure has not given it.”

“There are now a host of questions about the Obama administration’s self-professed killing-policy restrictions, how malleable they are in practice, and the extent to which the killing policy is unlawful,” Hina Shamsi, director of the ACLU’s National Security Project said in an email to The Intercept. “In response to those questions, the administration has responded with self-serving statements from anonymous government officials and deafening official silence.”

“The Obama administration has not only refused to disclose its legal memos justifying the killings of U.S and non U.S. citizens far from any battlefield,” Shamsi added. “It won’t even provide the public with basic information about the number and identity of the thousands of people who have died as a result of its lethal program.”